Prechargeable spring assembly for high-voltage bushings



B. N. BOWERS PRECHARGEABLE SPRING ASSEMBLY FOR HIGH-VOLTAGE BUSHINGS Dec. 30, 1952 Filed April 23, 1949 Inventor: Ben am'm Bowers,

His Attorney.

Patented Dec. 30, 1952 PRECHARGEABLE SPRING ASSEMBLY FOR HIGH-VOLTAGE BUSHINGS Benjamin N. Bowers, Pittsfield, Mass., assignor to General Electric Company, a corporation of New York Application April 23, 1949, Serial No. 89,314

1 Claim.

This invention relates to high voltage insulating bushings of the center-clamped type, and more particularly to a prechargeable spring assembly structure to aid in the assembly of such bushings.

The conventional high voltage insulator bushing comprises a central axial tube which may serve as a conductor or through which the high voltage conductor passes. the tube being surrounded by a number of concentric cylinders of insulating material and the whole assembly being surrounded by petticoat-type ceramic shells which form the external surface of the bushing. In the ordinary bushing one or a plurality of such ceramic shells is used in order to encompass the entire length of the bushing, the adjoining surfaces of these shells being sealed by gasket members.

There are several difierent ways of holding such insulating bushings in assembled relation. Some bushing structures are so constructed that the several shells which form the exterior surface of the bushing are provided with mating flanges which are bolted together so as to maintain the bushing tightly assembled.

Another method of maintaining the bushing in assembled relation is to provide a high force spring assembly at the top of the bushing structure to maintain pressure on the gasketed joints, and a center clamping nut which tightens onto a threaded portion of the center mounting tube to hold the entire structure in assembled relation. This invention is directed to an improvement which facilitates assembly of this latter type of bushing, namely, a bushing which is held in as sembled relation by means of a center clamping nut and a spring assembly.

In assembling a high voltage bushing of the center-clamped type, the ceramic shells are first loosely placed upon the center tube and after all of the component parts are in position the clamping nut is tightened down at the top of the entire structure to hold the various parts tightly in place in assembled relation.

- In constructing high voltage bushings of the type having a high force spring assembly for maintaining pressure on the gasketed joints, the problem arises that the force required to tighten down the nut at the top of the bushing assembly is so great due to the very high frictional losses in the threads of the clamping nut that it is extremely difficult to tighten the nut so as to maintain a satisfactory pressure on the gasketed joints.

It is an object of this invention. to provide a means to aid in tightening a center-clamped type of high voltage bushing assembly so as to eliminate the difficulties which have been heretofore encountered as just described.

My invention will be better understood from the following description taken in connection with the accompanying drawings and its scope will be pointed out in the appended claim.

In the drawing, Fig. 1 shows a center-clamped type of high voltage insulating bushing structure equipped with my new prechargeable spring assembly. Fig. 2 shows a cross-sectional detail view of my prechargeable spring assembly. Fig. 3 shows a modified form of a prechargeable spring assembly in accordance with my invention.

Referring now to the drawing, Fig. 1 shows a high voltage insulating structure comprising an axial mounting member or conductor I surrounded by upper and lower ceramic shells 2 and 3 and by intermediate support member 4. Member 4 is provided with a flange 5 which supports the entire bushing structure when the bushing is placed in position on the equipment with which it is used, such as, for example, a transformer tank. Axial mounting member I is rigidly attached at its lower end to bottom washer 8 by any suitable method, such as, for example, a threaded or welded connection.

On the interior of the bushing a number of concentric cylinders of insulating material surround the axial mounting member I and are supported below by the interior surface of shell 3. However, these insulating cylinders are not shown in the drawing since they have no convnection with the invention disclosed herein.

The interior of the bushing is filled with oil for insulating purposes. and to provide for expansion of this oil under high temperature conditions an expansion dome 1 is provided above upper shell 2. Above the expansion dome 1 but separated from it by a gasket is a prechargeable spring assembly 8 of my invention which will be described in more detail later. Above the prechargeable spring assembly 8, a clamping nut 9 is provided to hold the entire bushing structure in tightly assembled relation. The upper terminal of the bushing is shown at H].

As mentioned before, the various component parts of the assembly as just described are at first mounted loosely on axial mounting member 1, and gaskets are provided between the adjoining surfaces of the various sections in order to seal the respective joints. More specifically, the joint between lower shell 3 and support 4 is sealed by gasket H; the joint between flange 5 and upper shell 2 is sealed by gasket I2; the joint between shell 2 and dome I is sealed by gasket I3; and the joint between dome I and prechargeable spring assembly 8 is sealed by gasket I4. In addition, several other gaskets are used to seal the spring assembly 8, as will be described in more detail later.

In Fig. 2, a detail view of prechargeable spring assembly 3 and its relation to dome I, nut 9, and axial mounting member is shown.

The prechargeable spring assembly 3 is provided with a resilient metallic diaphragm l5 of toroidal shape made of a suitable material such as, for example, spun copper. Diaphragm I5 encloses a plurality of coil springs I6 which lie in annular grooves I? of annular spring guides I8 and I9. There may be one or several tiers of springs and spring guides. Spring guide i8 is positioned above spring guide I9, as will be seen from the drawing. Washer 2t serves as a bearing between the springs in upper spring guide it and the top of diaphragm I5. Spring guide I9 serves as a bearing between the lower tier of springs and the lower portion of the diaphragm. The lower tier of springs is held in compression by the lower surface of spring guide I8, while the upper tier of springs is held in compression by washer 29. A cover member 2| is positioned above the top of diaphragm I5, and gasket 22 serves as a seal between the cover 2| and the dia phragm I5.

Clamping nut S is positioned above cover 2| of prechargea-ble spring assembly 8. The clamping uut is screwed onto axial mounting member on the threads 23. between cover 2% and clamping nut 9.

As a means of applying precharging force to spring assembly 8, a clamping plate 25 is positioned above cover 2|. A series of studs 26 psitioned around the periphery of clamping plate 25 screw into tapped holes 2'! around the periphery of the upper surface of expansion dome l. Nuts 28 and washer 29 are placed on the studs above the clampng plate and serve to tighten the clamping plate, as will be hereinafter described.

The prechargeable spring assembly is utilized in the following manner: After the various component parts of the bushing are arranged loosely in place on axial mounting member I with the gaskets positioned in their proper places, as hereinbefore described, the bushing assembly is then ready to be tightened by means of clamping nut 9. However, as has been before explained, considerable force would have to be applied to tighten nut 9 and it might be almost impossible to tighten nut 9 down sufliciently to hold the bushing assembly in assembled relation due to the high internal friction of the threads on the outer surface of axial mounting member I and the inner surface of nut 5. However, due to the use of my prechargeable spring assembly 8, the bushing may be assembled with readily applied manual or mechanical force and without high frictional losses in the threads of the clamping nut 9 orstripping of the threads of the nut 3 or axial mounting member I.

The clamping operation is carried out in the fol-lowing manner: Clamping plate 25 is tightened down by means of nuts 28 on studs 26 until the gap 35 between the lower edge of cover 2| and the top of dome is reduced to a predetermined value. The clamping operation is performed by turning one nut a fraction of a turn at a time progressing circumferentially from one stud to the next so as to clamp the spring assembly very A gasket 24 provides a seal radually to the fully charged position. After this has been done, the central clamping nut 9 may then be easily screwed down to the desired positon on the axial mounting member I.

After the nut 9 has been screwed down to the desired position, the spring assembly inside diaphragm 15 may then be discharged by loosening the nuts on the studs a fraction of a turn at a time progressing in one direction around the circumference from one stud to the next. After the spring assembly has been discharged, the clamping plate may either be left in position on the bushing structure or it may be removed if desired.

A modified form of my prech-argeaible spring assembly is shown in Fig. 3. The construction disclosed in this figure differs from that shown in Figs. 1 and 2 principally in the fact that the prechargeable spring assembly is contained inside the dome of the bushing rather than outside the dome, as shown in Figs. 1 and 2.

As will be seen in Fig. 3, the bushing structure with which this modified spring assembly is associated comprises an axial mounting member or center tube 3| having a center conductor 32 contained therein. A washer 33 is placed at the top of center tube SI and supports nuts 34 and 35 between which flexible braid conductor 36 is clamped in contacting relationship with the up per end of center conductor member 32. The other end of the flexible braid conductor is attached to cover member 31 by means of bolt 38. Cover 31 is positioned over dome 39 and is held tightly in position by means of a plurality of bolts 40 provided with washers All and threaded into the upper part of dome 39. A seal is provided between cover member 3'! and dome 39' by means of gasket 42. The lower surface of the dome rests upon the upper surface of the top shell 43 of the bushing, and a seal is provided between these two adjoining surfaces by means of gasket 44.

As will be seen from Fig. 3, the prechargeable spring assembly is contained entirely inside the bushing and dome structure. The clamping element of the spring assembly comprises a clamp member 45 having a lower inner flange 46 which is in sliding fit with the exterior surface of center tube 3|. A nut 47 is positioned above the inner flange 45 of the clamp member 45 which is contiguous to center tube 3|. Nut 4'! has internal threads which engage the external threads on the upper portion of center tube 3|. The upper portion of clamp member 45 has another flange 48 which projects radially outwardly and is in contacting relation with the upper tier of springs 53, as will be hereinafter described.

The spring arrangement is in general similar to that disclosed in Figs. 1 and 2 and is comprised of one or more concentric tiers of spring guides #29 and springs 50. The lower surface of the bottom spring guide rests upon washer 52 which in turn rests upon the lower inside surface of dome 39. A plurality of studs 5| are threaded into washer 52. These studs are arranged around the circumference of the washer. The upper ends of the studs 5! extend through holes in the top flange 68 of the spring clamp 55, Nut 53 and washer 54 are positioned on the upper end of Each stud where the stud extends above the flange The clamping operation is performed by tightening the nut on each stud a fraction of a turn at a time progressing circumferentially from one stud to the next so as to clamp the spring assembly very gradually to the fully charged position. After the spring assembly is tightened down in the manner just described, nut on center tube 3| may then easily be tightened without the danger of stripping the threads either on the nut or on the center tube. After the nut ti has been tightened to the desired position, the clamp member 45 may then be discharged by loosening the nut 53 on each stud bl a fraction of a turn at a time, progressing in one direction around the circumference from one stud to the next.

In either the bushing structure of Figs. 1 and 2 or that of Fig. 3, the center tube or axial mounting member may be used as the conductor itself instead of having a center conductor inside the tube, and there may be some cases in which it would be desirable to use a rod instead of a tube as the central mounting member and also as a conductor.

From the foregoing it will be seen that the prechargeable spring assembly of my invention provides an easy and convenient means of tightening a high voltage electrical bushing structure of the type using a center clamping nut at the top of the structure and eliminates the great difficulty which is often encountered in tightening such bushing structures.

While there have been shown and described particular embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the invention and, therefore, it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

In an electrical insulating bushing of the liquid-filled type having at least one external insulating shell and a support member arranged. longitudinally about an axial mounting member, an expansion chamber for the reception of expanded liquid from said bushing, said expansion chamber being positioned axially outwardly of and immediately axially adjacent the axially outermost of said insulating shells, a clamping nut positioned at the end of said mounting member axially outwardly of said expansion chamber, a substantially totally enclosed spring assembly and a cover member for said spring assembly coaxially positioned between the axially outermost surface of said expansion chamber and the axially innermost surface of said clamping nut, an enclosure means for said spring assembly comprising a generally toroidal-shaped hollow diaphragm member of resilient metal coaxially positioned about said mounting member, said diaphragm member containing at least two tiers of annular-shaped axially-displaced spring holders,

with a plurality of spiral springs circumferentia y positioned about and supported by said an ng holders within said diaphragm, said cover member having a substantially annular-shaped portion perpendicular to the axis or" said mounting member, said annular-shaped portion of said cover member being made of relatively strong, inflexible material, said annular-shaped portion of said cover member having its axially innermost surface positioned adjacent the axially outermost surface of said diaphragm, the axially outermost surface of said annular-shaped potion of said cover member being in contact Y in the axially innermost surface of said clampin a sealing gasket interposed between said adjacent surfaces of said annular-shaped portion of said cover member and said diaphragm, a sealing gasket interposed between the axially innermost sur face of said diaphragm and the axially outermost surface of said expansion chamber, a gasket member interposed at the joint between clamping nut and the axially outermost surface of said annular-shaped portion of said cover member, said clamping nut being recessed to receive said gasket, a clamping plate coaxially positioned axially outwardly of said cover member for applying compressive force to the axially outermost surface of said annular-shaped portion of said cover member before positioning said clamping nut, said clamping plate being circumferentially apertured to receive a plurality of axially-extending threaded stud members, the axially innermost end of each of said stud members being threadedly engaged with the axially outermost surface of said expansion chamber, the axially outermost end of each of said stud members passing through one of said apertures in said clamping plate, with a threaded nut member positioned on the axially outermost end of each of said stud members to permit tightening said clamping plate against the axially outermost surface of said cover member to compress said spring assembly, said clamping plate being releasable after said clamping nut is positioned.

BENJAMIN N. BOWERS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,572,402 Mathwig Feb. 9, 1926 1,988,151 Austin Jan. 15, 1935 2,117,697 Brandt May 17, 1938 2,135,321 Brandt Nov. 1, 1938 2,228,089 Skvortzofi Jan. 7, 1941 2,292,031 Arnold Aug. 4, 1942 2,395,426 Petrovich Feb. 26, 1946 

